The barrier effect of a WxTa(1-x) nanolayer on formation of single-texture CoSi2 on Si(100)

We have studied the phase formation of a CoSi2 layer by solid-state reaction of ternary Co/WxTa(1- x)/ Si( 1 0 0) systems. The effect of cosputtered WxTa(1- x) nanometric interlayers, with different values of x ( 0, 0.25, 0.5, 0.75 and 1), on the degree of texturing of a CoSi2 layer and disilicide formation of the refractory metals has been investigated. The annealed samples, in a temperature range of 400 - 1000 degrees C, were analysed by x-ray diffraction, sheet resistance measurement, scanning electron microscopy, and energy-dispersive x-ray techniques. Using W0.25Ta0.75 and W interlayers, the best ( 1 0 0) texture of the CoSi2 layer with a thermal stability in the range of 900 - 1000 degrees C was produced. In the Co/W/Si system, a considerable amount of WSi2 is formed as a cap layer, while a nearly negligible amount of refractory metal disilicide is formed in the Co/W0.25Ta0.75/Si system. Study of the growth kinetics shows that the activation energies of CoSi2 formation in these two systems are greater than those of other thermally stable systems. The mechanism of single-texture formation of a nanothickness CoSi2 layer has been explained on the basis of controlling Co-Si interdiffusion via the intermediate layers.